The Standardized
Field Sobriety Test (SFST) is a battery of three
tests administered and evaluated in a standardized
manner to obtain validated indicators of impairment
and establish probable cause for arrest. These
tests were developed as a result of research
sponsored by the National Highway Traffic Safety
Administration (NHTSA) and conducted by the
Southern California Research Institute. A formal
program of training was developed and is available
through NHTSA to help police officers become
more skillful at detecting DWI suspects, describing
the behavior of these suspects, and presenting
effective testimony in court. Formal administration
and accreditation of the program is provided
through IACP.

The three tests
of the SFST are:
1. the horizontal gaze nystagmus (HGN)
2. the walk-and-turn
3. the one-leg stand.

These tests are administered systematically
and are evaluated according to measured responses
of the suspect.

HGN Testing

Horizontal gaze
nystagmus is an involuntary jerking of the eyeball
which occurs naturally as the eyes gaze to the
side. Under normal circumstances, nystagmus
occurs when the eyes are rotated at high peripheral
angles. However, when a person is impaired by
alcohol, nystagmus is exaggerated and may occur
at lesser angles. An alcohol-impaired person
will also often have difficulty smoothly tracking
a moving object. In the HGN test, the officer
observes the eyes of a suspect as the suspect
follows a slowly moving object such as a pen
or small flashlight, horizontally with his eyes.
The examiner looks for three indicators of impairment
in each eye: if the eye cannot follow a moving
object smoothly, if jerking is distinct when
the eye is at maximum deviation, and if the
angle of onset of jerking is within 45 degrees
of center. If, between the two eyes, four or
more clues appear, the suspect likely has a
BAC of 0.10 or greater. NHTSA research indicates
that this test allows proper classification
of approximately 77 percent of suspects. HGN
may also indicate consumption of seizure medications,
phencyclidine, a variety of inhalants, barbiturates,
and other depressants.

Divided Attention Testing

The walk-and-turn
test and one-leg stand test are "divided
attention" tests that are easily performed
by most sober people. They require a suspect
to listen to and follow instructions while performing
simple physical movements. Impaired persons
have difficulty with tasks requiring their attention
to be divided between simple mental and physical
exercises. In the walk-and-turn test, the subject
is directed to take nine steps, heel-to-toe,
along a straight line. After taking the steps,
the suspect must turn on one foot and return
in the same manner in the opposite direction.
The examiner looks for seven indicators of impairment:
if the suspect cannot keep balance while listening
to the instructions, begins before the instructions
are finished, stops while walking to regain
balance, does not touch heel-to-toe, uses arms
to balance, loses balance while turning, or
takes an incorrect number of steps. NHTSA research
indicates that 68 percent of individuals who
exhibit two or more indicators in the performance
of the test will have a BAC of 0.10 or greater.
In the one-leg stand test, the suspect is instructed
to stand with one foot approximately six inches
off the ground and count aloud by thousands
(One thousand-one, one thousand-two, etc.) until
told to put the foot down. The officer times
the subject for a 30 seconds. The officer looks
for four indicators of impairment, including
swaying while balancing, using arms to balance,
hopping to maintain balance, and putting the
foot down. NHTSA research indicates that 65
percent of individuals who exhibit two or more
such indicators in the performance of the test
will have a BAC of 0.10 of greater. The effectiveness
of SFST in court testimony and evidence depends
upon the cumulative total of impairment indicators
provided by the three-test battery. The greater
the number of indicators, the more convincing
the testimony. Because SFST is administered
according to national standards and is supported
by significant research, it has greater credibility
than mere subjective testimony.

Alternative
Testing Methods

Sometimes,
an officer will encounter a disabled driver
who cannot perform the SFST. In such cases,
some other battery of tests such as counting
aloud, reciting the alphabet, or finger dexterity
tests may be administered. If the proper motions
are filed, these test are usually not admissible
at trial.